GB2237388A - System for detecting combustion condition of an internal combustion engine - Google Patents

Abstract

To detect and correct for uneven running, especially when idling, a period when the combustion of an engine is not performed is detected at two points before and after the top dead center of each cylinder in the expansion stroke. Engine speeds in both the periods are detected and the speed difference between the detected periods is calculated. Mean speed difference is calculated over a number of cycles of the engine using a weighting system. The mean speed difference is compared with a predetermined limit value, whereby the combustion condition of the corresponding cylinder is investigated. The parameter detected may alternatively be crank acceleration, and the system is used to control ignition timing to achieve smooth running. The system also uses detected values of coolant temperature, exhaust oxygen, road speed, knocking, and mass air flow. <IMAGE>

Description

4 2! 2: CB -7 3 a a 1 System for detecting Combustion Condition of an

Internal Combustion Engine The present invention relates to a system for detecting the condition of the combustion in a cylinder of an internal combustion engine and which is available for controlling the ignition timing of the engine.

It is desirable to control the idling speed of the engine to a low speed in accordance with requirement for fuel economy and reduction of engine noise. However, at low idling speeds fluctuation of the engine speed occurs and hence reduction of the starting characteristics of a motor vehicle driven by the engine. It is generally believed that differences among the combustion conditions of respective cylinders of a multicylinder engine cause the fluctuation of the idling speed. The fluctuation of the combustion conditions are caused by the following differences.

The difference in distribution rate of intake air caused by complicated configuration of the intake manifold and by interference between the intake-air distributed to respective cylinders; 2) The difference of combustion temperatures in respective cylinders which is caused by a disposition of a coolant passage; 3) The difference in capacity of combustion chambers, shape of the piston etc, which are caused by 2 manufacturing tolerances; 4) The difference in air-fuel ratio in respective cylinders which is caused by differences in the amount of injected fuel.

It will be understood that the idling speed becomes constant by rendering the above described combustion conditions uniform.

JP-A-62-55461 discloses a system for detecting combustion conditions in respective cylinders. The system has pressure sensors provided at every cylinder for detecting pressure in the cylinder. The combustion condition of each cylinder is estimated from a peak in the pressure detected by each pressure sensor. However, the system is costly because pressure sensors are comparatively expensive. In addition, the cylinder head of the engine has to be drilled for attaching the pressure sensors. Furthermore, it is difficult to apply the system to conventional engines.

On the other hand, JP-A-59-82534, and laid open Japanese Utility Model Applications 63-196448, 63-198473, and 63-202771 disclose systems for idling speed control. The systems detect instantaneous engine speeds before and after combustion in each cylinder, and the speed difference A Ni between the two engine speeds is obtained from every cylinder. The systems control engine parameters so that the speed difference A Ni becomes zero, thereby causing the engine speed to 3 be constant.

The systems calculate a deviation of the speed difference A Ni from a standard value which is an average value of speed differences at all cylinders. However, the average value is liable to fluctuate in accordance with engine combustion conditions. As a result, other combustion condition factors than the detecting cylinder are included in the combustion conditions for the cylinder, so that the combustion conditions can not be accurately detected. Therefore, the idling speed is not controlled to a predetermined value, because ignition timing and quantity of injected fuel for each cylinder are determined on the basis of the estimated combustion conditions.

An object of the present invention is to provide a system which may accurately detect the combustion condition of the or each cylinder so that ignition timing of each cylinder so as to control idling speed to a predetermined value can be properly controlled.

According to a first aspect of the invention, a system for detecting the condition of the combustion in a cylinder of an internal combustion engine, said engine having a crank angle sensor for producing a crank angle signal representing the angular position of the crankshaft of the engine and a cam angle sensor for A 1 4 producing a cam angle signal representing the angular position of the camshaft of the engine. Comprises:

detecting means for detecting a period before and a period after top dead centre of the cylinder in the expansion stroke and for producing signals representing said respective periods; detector means responsive to said period signals for detecting a parameter representing the motion of the engine during each of the periods and for producing for each of the periods a signal which represents said parameter, difference calculator means for calculating from said signals the difference in the parameter in the periods; a mean difference calculator for calculating a mean value of said differences; and means for comparing said mean value with predetermined limit values to determine the condition of the combustion in the cylinder.

According to a second aspect of the invention a system for detecting the condition of the combustion in each cylinder of a multi-cylinder internal combustion engine having a crank angle sensor for producing a crank angle signal representing the angular position of the crankshaft of the engine and a cam angle sensor for producing a cam angle signal representing the angular position of the camshaft of 1 A the engine, comprises:

discriminating means responsive to said cam angle signal for detecting in turn each cylinder in its expansion stroke and for producing a signal representing said cylinder; period detecting means responsive to said cylinder signal for detecting periods before and after top dead center of each cylinder in its expansion stroke, and for producing period signals representing said respective periods; detector means responsive to said period signal for detecting a parameter representing the motion of the engine during each of said periods and for producing respective condition signals; difference calculator means for calculating from the signals the difference in the parameter in said periods; a mean difference calculator for calculating a mean difference of said differences; and means for comparing said mean difference with predetermined limit values thereby determining the condition of the combustion in the cylinder.

The parameter which is detected may be the speed of the engine, or it may be the angular velocity of the crankshaft of the engine, or it may be the angular acceleration of the crankshaft of the engine.

In order that the invention may be more a 6 readily understood, it will now be described with reference to the accompanying drawings in which Fig. 1 is a schematic illustration of a system according to the present invention; Figs. 2a to 2c show a block diagram of an electronic control unit; Fig. 3 shows a crankshaft disk with a crank angle sensor provided in the system; Fig. 4 shows a camshaft disk having a cam angle sensor provided in the system; Fig. 5 shows a map of a basic ignition timing; Fig. 6 is a time chart showing a variation of inner pressure of each cylinder, a crank angle pulse, a cam angle pulse and engine speed; Fig. 7 shows a flowchart for estimating combustion condition of the cylinder; Fig. 8 shows the flowchart showing the ignition timing control of the system; Figs. 9a to 9c is a block diagram showing the system of a second embodiment of the present invention; Figs. 10a and 10b show the flowchart showing an operation for detecting the combustion condition of the second embodiment; Fig. 11 is a time chart showing a relation of a crank pulse, a cam pulse, engine speed and angular Y1 6a acceleration of the second embodiment; Figs. 12a to 12c show the block diagram of a third embodiment of the present invention; Fig. 13 is the flowchart showing the operation for detecting the combustion condition of the third embodiment; Figs. 14a to 14c show the block diagram of a fourth embodiment of the present invention; Fig. 15 is the flowchart of the operation for detecting the combustion condition of the fourth embodiment; and Fig. 16 is the flowchart of the operation for the ignition timing control of the fourth embodiment.

Referring to Fig. I showing a horizontal opposed type four-cylinder engine 1, a cylinder head 2 of the engine 1 has intake ports 2a and exhaust ports 2b which are communicated with an intake manifold 3 and an exhaust manifold 21, respectively. A spark plug 11 having an ignition coil Ila is located in each combustion chamber formed in the cylinder head 2. A throttle chamber 5 having a throttle valve 5a is communicated with the intake manifold 3 through an air chamber 4. The throttle chamber 5 is 1 7 communicated with an air cleaner 7 through an intake pipe 6.

An intake air quantity sensor 8 (hot wire type air-flow meter) is provided in the intake pipe 6 downstream of the air cleaner 7. A throttle position sensor 9a is provided for detecting an opening degree of the throttle valve Sa. An idle switch 9b is provided adjacent the throttle position sensor 9a for detecting the throttle valve Sa at an idling position. Fuel injectors 10 are provided in the intake manifold 3 adjacent every intake port 2a. Fuel in a fuel tank 13 is supplied to the injector 10 through a fuel passage 12 having a pump 14. A crankshaft disk 15 is secured to a crankshaft lb of the engine 1. A crank angle sensor 16 (magnetic pickup) is provided adjacent the crankshaft disk 15 for detecting crank angles.

is A camshaft disk 17 is secured to a camshaft lc for detecting camshaft angles. The camshaft Ic rotates once while the crankshaft lb rotates twice. A cam angle sensor 18 is provided adjacent the camshaft disk 17.

Referring to Fig. 3, cylinders of the engine 1 are divided into two groups. A first group consists of No.1 and No.2 cylinders, and a second group consists of No.3 and No.4 cylinders. Top dead centers of the two cylinders in each group has the same timing. The crankshaft disk 15 has a pair of projections 15a disposed at a crank angle el before the top dead center (BTDC), a pair of projections 15b disposed at k 1 1 8 a crank angle e2 (BTDC), and a pair of projetdisposed at a crank angle e3 (BTDC) The proje, 15b, 15c are provided for detecting proper timings calculating the instantaneous engine speeds. A perio is calculated from an elapsed time between the projecti Olk 15a and 15b (here f = llw w: angular velocity). A perioc, f2.3 is calculated from the elapsed time between the projections 15b and 15c. The crank angle e2 of the projection 15b represents a reference crank angle for determining an ignition timing.

Referring to Fig. 6. the crank angles e2 and 93 of the projections 15b and 15c are determined at positions before and after an ignition timing (time) ADV at idling of the engine 1. The ignition timing at the idling of the engine 1 is usually determined at BTDC 200CA. Even if the spark plug 11 is ignited at that timing, a combustion pressure is not rapidly increased till BTDC 10CA.

Furthermore, an opening time of the exhaust valve of each cylinder is set at a slightly retarded timing from the ignition reference crank angle e2. Since the combustion pressure immediately after opening the exhaust valve is rapidly reduced, there is no influence of thecombustion pressure at the crank angle 93.

Consequently, if the crank angle W of the projection I 9 t 15c is set at an advanced timing from the BTDC 10'CA, a period between the crank angles BTDC 92 and 03 of the projections 15b and 15c is not influenced by the combustion pressure of each cylinder. In other words, in the period between 02 and e3, there is no influence of physical work caused by combustion.

When the crankshaft disk 15 rotates, the crank angle sensor 16 detects positions of the projections 15a, 15b and 15c and produces signals in a form of pulses.

Referring to Fig. 4, the camshaft disk 17 is provided with a projection 17a, a pair of projections 17c and 17c', a projection 17a', and three projectons 17b, 17b' and 17b" on an outer periophery thereof. Projections 17a, 17b, 17c and 17a' are positioned according to a firing (igniting) order of the cylinder. Namely, the projections 17a and 17a' represent No.3 and No.4 cylinders, disposed at a cam shaft angle e4 after the top dead center (ATDC) in the compression stroke, the projections 17b to 17b" represent No.1 cylinder and the projection 17b is disposed at a cam angle ATDC 65, and the projections 17c and l7c' represent No.2 cylinder and the projection 17c is disposed at a cam angle ATDc e6. The cam angle sensor 18 detects the projections to produce a cam angle signal representing a number of the cylinder in the form of the pulses.

i In the embodiment, the angle el is 97CA, angle 02 is 65CA, 93 is 100CA, 94 is 20CA, e5 is 5CA, e6 is 200CA and 9(2-3) is 550CA.

As shown in Fig. 6, when the cam angle sensor 18 detects the position of the projection 17b at angle es, it is determined that a crank angle pulse signal produced by the crank angle sensor 16 after the cam angle pulse signal of the angle e5 represents the top dead center of No.3 cylinder. When the cam angle sensor 18 detects the projection 17a at angle e4, it is determined that a crank pulse signal produced after the cam signal 04 represents the top dead center of No.2 cylinder.

Similarly, the crank pulse signal produced after the cam pulse signal of the projection 17c at angle 96 represents No.4 cylinder and the crank pulse signal produced after the cam pulse signal of the projection 17a at angle 04 represents No.1 cylinder.

Furthermore, the crank pulse signal produced after the cam pulse signal represents a basic crank angle 91 of the corresponding cylinder.

In order to detect a knocking, a knock sensor 19 is mounted on a body of the engine 1 to detect oscillation of the engine 1. A coolant temperature sensor 20 is provided in a coolant jacket (not shown) of the engine 1.

1 An 0 2- sensor 22 and a catalytic converter 23 are provided in an pxhaust passage communicated with the exhaust manifold 21. Numeral 24 designates a vehicle speed sensor.

An electronic control unit 31 having a microcomputer comprises a CPU (central processing unit) 32, a ROM 33, a RAM 34 and an input/output interface 35, which are connected to each other through a bus line 36. Sensors 8, 9a, 16, 18, 19, 20, 22, 24 and the idle switch 9b are connected to an input port of the input/output interface 35. An output port of the interface 35 is connected to the spark plug 11 of the corresponding cylinder through an igniter 25 and a driver 38 which is connected to injectors 10.

Control programs and fixed data such as an ignition timing map are stored in the ROM 33. Octput signals of the sensors are stored in the RAM 34. The RAM 34 stores output signals of the sensors after processing data in the CPU 32.

The CPU 32 calculates a fuel injection pulse width and an ignition timing in accordance with the control programs in the ROM 33 and based on various data in the RAM 34.

Referring to Fig. 2, the control unit 31 comprises an input data calculating section 41, a cor-bustion condition detecting section 42 and an ignition tir-ing calculating section 43. The input data calculating section 41 has cylinder discriminating means 41a to which the crank pulse signal of the crank angle sensor 16 and the cam pulse signal L 12 of the cam angle sensor 18 are applied. The means 41a discriminates the number of the cylinders No. i (i=l, 3, 2, 4) in accordance with the crank pulse generated after the cam pulse based on the number of the cam pulses of the projections.

Crank angle signal discriminating means 41b is applied with the crank angle signal and the cam angle signal from the sensors 16 and 18, the crank angle signal discriminating means 41b discriminates the crank angle signal generated after the cam angle signal dependent on the projections 15a, 15b and 15c. The signal is applied to a frequency calculator 41c where an elapsed time tl.2 between the crank angle el of the projection 15a and the crank angle e2 of the projection 15b is measured. The period (repetition rate) fl.2 is calculated in accordance with the elapsed time tl.2 and included angle (el-92) (:;- 1. 2 = d t d ( 8 1 - 6 2)) Then, an elapsed time t2.3 between the crank angle 02 of the projection 15b and the crank angle 93 of the projection 15c is measured. The period f2.3 is calculated in accordance with the elapsed time t2.3 and included angle (e2-e3) :F 2. 3 = d t 2. 3 d ( 6 2 - 6 3) As aforementioned, the detecting period between the angles e2 and G3 is a zone between the combustion of the preceding cylinder and the combustion of the following cylinder, in which the work due to the combustion is not performed. Therefore, the engine speed does not rapidly k 13 change in the period, and hence the period f23 calculated in accordance with angles e2 and e3 is not affected by the combustion.

A period signal is applied to an engine speed calcualtor 41d for calculating engine speeds N1.2 and N NEW based on the periods fl.2 and f23 N 1. 2--- 6 0 -2 6 0 ? 7r - 1. T-, N H E W - 2 7C:f Z. -r).

Idling state determining means 41e is provided for determining the idling state of the engine in accordance with signals from the vehicle speed sensor 24 and the idle switch gb. The idling state determining means 41e determines idling of the engine 1 when the vehicle speed is zero and an on-signal is applied form the idle switch gb.

An intake air quantity calculator 41f calculates an intake air quantity in accordance with an output signal from the intake air quantity sensor 8.

The combustion state detecting section 42 comprises an engine speed difference calculator 42a which calculates an engine speed difference AN&(i=1,3,2,4) of the corresponding cylinder at the idling of the engine. When the idling of the engine 1 is determined at the idling state determining means 41e, the calculator 42a reads the engine speed N NEW stored in a predetermined address of the memory (RAM) 34, which is calculated based on the period f2.3 at the engine speed calculator 41d, and reads an engine speed N OLD stored in the memory, which is calculated in the last routine based 11 1 14 on the period f23. The calculator 42a calculates speed difference ANi of the corresponding cylinder No.i discriminated at the cylinder discriminating means 41a in accordance with the difference between the engine speeds N NEWandNOLD. (ANi =N NEW -NOLD).

The engine speed N NEW is stored in the memory 34 to update the engine speed N OLD (N OLD,- N NEW).

The program for operating the control system starts at every 180 degree of the crankshaft 16. Consequently, the 10 engine speed N NEW calculated on the basis of the period f23 performed for a cylinder of one of the groupes is common to one of the cylinders of the other groups. For example, the engine speed N NEW of No.1 cylinder corresponds to the last engine speed N OLD for the No.3 cylinder.

If each engine speed common to both cylinders is represented as N4.1, N1. 3, N3.2, and N2.4, respectively, the engine speed difference of each cylinder is expressed as follows.

AN1 = N1.3 - N4.1 AN3 = N3.2 - N1.3 AN2 = N2.4 - N3.2 AN4 = N4.1 - N2.4 An experiment by the applicant proved that the engine speed difference ANi correlates with an indicated mean is effective pressure, namely the combustion conditions of the cylinder. Thus, the conditions of the combustion of each cylinder can be estimated by the speed difference ANi.

The relationship between the speed difference ANi and the indicated mean effective pressure is described as follows.

The operation of the engine 1 is represented by an equation as follows.

1 2 7r d N T f (1) 6 0 d t where 1: a moment of inertia N: engine speed Ti: indicated torque is Tf: friction torque.

Simplyfying the equation (1).

d N cc T i - T f d t Further, substituting the pressure for torque, d N W. p i - P f .... (2) .... (3) where Pi: the indicated means effective pressure 16 1 Pf: effective pressure due to friction loss.

In accordance with the experiment, if the crank angle for detecting the engine speed and the duration of the crank angle for calculating the speed are provided at angles 02.3, namely before and after the combustion of the cylinder, dN/dt in the equation (3) is obtained on the basis of the engine speed difference ANi and a change with time AT (180'CA) there- between in the four-cycle engine. As a result, a close correlation can be obtained between the speed difference ANi and the effective pressure.

in this case, variation of the time AT can be ignored and if a friction loss effective pressure Pf is constant, the following equation is obtained from the equation (3).

is A N = K X P i + P F ...... (4) where K and Pf are constants.

Thus, by obtaining the-speed difference AN of each cylinder, the indicated mean effective pressure Pi, namely the combustion conditions of each cylinder can be estimated. If the speed difference ANi at each period relative to the cylinder approaches zero, the combustion condition of each cylinder can be uniformed. 25 In the equation (3), if Pi is constant and regarded as a constant C, and X is a proportional constant, dN/dt is:

17 d N. K - P i - C d t ...... (5) Thus, the indicated mean effective pressure Pi is obtained if the constants K and C are obtained.

In accordance with the equation (5), the indicated mean effective pressure Pi can be more accurately estimated from the speed difference ANi.

The engine speed difference A Ni is applied to a mean speed difference calculator 42b in which a means speed difference AN Ai at the detecting period for the corresponding cylinder No. i is calculated in accordance with the speed difference ANi and the last means speed difference ANAi(-1) stored in a predetermined address of the memory 34 through weighted mean by the equation as follows.

2 r X N A 2 r where r is weighted coefficient.

The mean speed difference at first time is zero.

The mean speed difference ANAi is calculated at every detecting period for respective cylinders.

The mean speed difference ANAi is calculated through the weighted means so that measuring error of the corresponding cylinder and the variation caused by temporary fluctuation of the engine speed can be corrected. The 4 18 i calculating operation which will be described hereinafter is performed based on clata for each cylinder.

The mean speed difference ANAi is applied to a combustion condition estimating means 42c having fixed upper limit determining means 42d, and fixed lower limit determining means 42e. The mean speed difference ANAi is first fed to the fixed upper limit determining means 42d. The mean difference ANAi is compared with a predetermined fixed upper limit speed difference ANu which is previously provided in the means 42d. When ANAi 'c ANu, the mean speed difference ANAi is applied to the fixed lower limit determining means 42e and compared with a fixed lower limit speed difference ANL which is previously provided in the means 42e.

These upper and lower fixed limit values ANu and ANL are determined on the basis of upper and lower determining values of the indicated mean effective pressure obtained by the experiment.

When ANAi ANL at the 'fixed lower limit determining means 42e, namely the mean speed difference ANAi is within the range of the fixed limit speed difference ( ANu ANAi ANL), a signal is applied to mean speed difference update means 42f. The update means 42f operates to update the last mean speed difference ANAi (- 1) stored in the memory 34 with the mean speed difference ANAi ( ANAi(-1) - ANAi).

19 i The ignition timing calculating section 43 comprises engine load determining means 43a in which an engine load Tp is calculated or derived from a lookup table based on the engine speed N1.2 from the engine speed calculator 41d and an intake air quantity Q from the intake air quantity calculator 41f. In the embodiment, the engine load Tp is calculated by the equation (Tp = K x QIN K: constant).

The engine load Tp is applied to basic ignition timing providing means 43b which is applied with engine speed N1.2.

In the means 43b, an ignition timing lookup table MPOB is retrieved in accordance with the engine speed N1.2 and the engine load Tp to derive a basic ignition timing (angle) 9B.

Fig. 5 shows the lookup table MPGB of the basic ignition timing is provided in the ROM 33 in which fixed data are stored. The table is a three-dimensional table in accordance with the engine load Tp and the engine speed N1.2 as parameters. The basic ignition timings which are previously provided by the experiment are stored in each crossing point.

The basic ignition timing GB is applied to ignition timing providing means 43h in which the basic ignition timing 9B is corrected to provide an ignition timing 91G. The ignition timing providing means 43h is applied with signals from the idling state determining means 4le and knock control value setting means 43c.

is 1 The knock control value setting means 43c is provided for setting a knock control value ONK for preventing the engine 1 from knocking. The means 43c is applied with an output voltage from the knock sensor 19. The output voltage is compared with a reference voltage which is previously provided in the means 43c. When the output voltage is lower than the reference voltage, no knock condition is determined. The knock control value ONK is advanced by a predetermined crank angle e (ONK.- + G).

When the output voltage is higher than the reference voltage, the occurrence of the knock is determined. The control value eNK is retarded by the angle 9 for sufficiently preventing the engine 1 from knocking (eNK e).

The basic ignition timing (angle) eB is corrected in accordance with the knock control value eNK to provide the ignition timing (angle) eIG for the corresponding No. i cylinder (elG -'- eB + eNK).

When the idle signal from the means 41e is applied to the means 43h, the basic ignition timing eB is corrected in accordance with a learning correcting coefficient LADVi stored in the memory 34 and the knock control value GNK to provide the ignition timing (eIG4-GB + eNK + LADVi).

The ignition timing calculating section 43 is provided with learning coefficient limit determining means 43d having learning coefficient retard angle limit determining means 43e and learning coefficient advance angle limit determining 21 t means 43f. The retard angle limit determining means 43e and the advance angle limit determining means 43f are provided with a retard angle limit correcting value LmtRTD and an advance angle limit correcting value LmtADV for each cylinder, respectively. Each of the limit determining means 43e and 43f compares the learning correcting coefficient LADVi for each cylinder stored in the memory 34 with the correcting value LmtRTD(LmtAM). When it is determined that the learning correcting coefficient LADVi exceeds the retard angle limit correcting value LmtRTD (LADVi" LmtRM), a signal is applied to each cylinder learning correcting coefficient update means 43g. The update means 43g operates to update the learning correcting coefficient LADVi stored in the memory 34 with the correcting value LmtRM (LADVi <- LmtRTD).

When it is determined that the learning correcting coefficient LADVi exceeds the advance angle limit correcting value LmtADV(LADVi LmtADV), the learning correcting coefficient LADVi is updated wtih the value LmtADV (LADVi LmtADV). Thus, the learning correcting coefficient LADVi is provided within the range between the limit correcting values LmtRTD and LmtAM.

The learning correcting coefficient update means 43g is further applied with the signals from the fixed upper limit determining means 42d and the fixed lower limit determining means 42e of the combustion condition estimating means 42c.

1 22 1, When ANAi> ANu at the means 42d, which means that the combustion condition is extremely good, the learning correcting coefficient LADVi is corrected to retard with a predetermined crank angle C (for example, C = ICA). The update means 43g operates to update the learning coefficient LADVi with the retarded coefficinet (LADVi-f- LADVi-C).

When ANAi<A NL at the fixed lower limit determining means 42e, i.e. when the combustion condition is bad, the learning coefficient LADVi is corrected to advance with the crank angle C. The coefficient LADVi is updated with the advanced coefficient (LADVi (-LADVi + C). The ignition timing OIG is applied to an ignition time setting means 43i

which is applied with the period fl.2 calculated at the frequency calculator 41c. The means 43i operates to set an ignition time ADV in accordance with the ignition timing eIG and the period fl.2 (ADV = eIG x fl.2) The ignition time ADV is set in a timer 43j which starts measuring time in accordance with the crank angle signal representing the reference angle e2 detected by the means 43b as a trigger signal. When the timer reaches a set ignition time, a spark signal is applied to an ignition selecting means 43k. The means 43k produces a signal which is applied to the ignitor 25 of the corresponding cylinder No. i to cut off the circuit for primary winding of the ignition coil lla.

23 In the learning coefficient limit determining means 43d, if LADVi LmtRM or LADVi LmtADV is determined at the means 43e or 43f, a signal is applied to the mean speed difference update means 42f for resetting the mean speed difference ANAi ( A NAi <-- 0). Thus, the update means 42 f operates to update the last mean speed difference ANAi(-1) in the memory 34 by the reset means speed difference ANAi A NAi (0) ( ANAi (-1) - 0).

Namely, if the learning coefficient LADVi exceeds the range between the limit correcting values LrntRTD and LmtADV, the update means 43g determines both of the correcting values as the limit values of the learning coefficient. Consequently, the means speed difference ANAi is reset to prevent an error which will be produced in the calculated result at the calculator 42b.

The operation of the system for estimating the combustion condition of the cylinder at idling of the engine is described hereinafter with reference to a flowchart of Fig. 7. The control program-is executed on each individual cylinder.

At a step S101, a vehicle speed and an output signal of the idle switch are read during a driving state of the vehicle. At a step S102, the idling state is determined. When the vehicle speed is zero and the idle switch is turned on, the idling state is determined, and the program goes to a step S103. When the vehicle speed is not zero and the 24 i idle switch is turned off, the driving state of the vehicle is determined and the program terminates the routine.

At the step S103. the cylinder No. i in the expansion (combustion) stroke is discriminated in accordance with the cam pulses from the cam sensor 18. At a step S104, the crank pulses from the crank angle sensor 16 at crank angles BTDC e2 and e3 are discriminated with reference to the carn pulse at crank angles BTDc e2 and e3.

At a step S105, the period f2.3 is calculated in accordance with the elapsed time t2.3 between crank pulses discriminated at the step S104 and the included angle (92 - e3) f 2,3 = d t 2.31 / d 2 L9 3) At a step S1061 the engine speed N NEW is calculated in accordance with the period f2.3 NNEW -6 0/ ( 2 f -2.3 is At a step S107, in accordance with the difference between the engine speed N NEW and the engine speed N OLD calculated in the last routine, the engine speed difference A Ni in the non-working period (e2 - e3) (Fig. 6) is calculated (t Ni -N NEW -N OLD). At a step S108, the engine, speed N OLD stored in the memory is updated with the engine speed N NEW (N OLD x- N NEW).

At a step S109, the mean speed difference ANAi is calculated through the weighted means based on the speed difference ANi and a means speed difference 6NAi(-1) in the last routine ( dNAi- ( ( 2 r _ 1) XANAi(A)+,dN 9:) /2) - 1 1 At a step SI 10. the mean speed difference A NAi is compared with fixed an upper limit speed difference A NU. When A NAi > A Nu, it is determined that the combustion condition is extremely good. The program goes to a step S111 where the learning correcting coefficient LADVi stored in the RAM 34 is updated with the coefficient LADVi corrected by retarding with the crank angle C (C=1CA) (LADVi - LADVi-C).

At a step S112, the learning coefficient LADVi obtained at the step S111 is compared with the retard angle limit correcting value LmtRTD. When LADVi > lantRTD, it is determined that the coefficient LADVi does not reach the retard angle limit. The program goes to a step S119.

At the step S112, when LADVi LmtRTD, the coefficient LADV-4 reaches the retard angle limit. Thus, the program goes to a step S113 where the learning coefficient LADVi stored in the memory is updated with the correcting value lintRTD (LADVi f- LmtRM).

On the other hand, at the step S110, when ANAi < A Nu, the program goes to a step S114 where the mean speed difference ANAi is compared with the fixed lower limit speed difference ANL. When ANAi< ANL, it is determined that the combustion condition is bad. The program goes to a step S115 where the learning correcting coefficient LADVi in the RAM 34 is updated with the coefficient LADVi corrected with the advanced crank angle C (LADVi 4- LADVi + C).

26 At a step S116, the learning coefficient LADVi obtained at the step S115 is compared with the advance angle limit correcting value LmtADV. When LADVi< Lmt ADV, it is determined that the coefficient LADVi does not reach the advance angle limit. The program goes to a step S119.

At the step S116, when LADVi 1 Lmt ADV, the coefficient LADVi reaches the advance angle limit. Thus, the program goes to a step S117 where the learning coefficient LADVi stored in the memory is updated with the correcting value 10 LmtADV (LADVi -LmtADV).

At the step'S114, when ANAi > ANL, it is determined that the mean speed difference ANAi is in the range 6 Nu > A NAi > LNL), the program proceeds to the step S119.

At a step S118, the means peed difference ANAi is reset ( ANAi 6 0).

At the step S119, the last mean speed difference ANAi (-1) stored in the RAM is updated with the mean speed difference ANAi calculated at the step S109 or reset at the step S118.

The operation for controlling the ignition timing will be described with reference to the flowchart of Fig. 8. The ignition timing control is executed at every cylinder.

At a step S201, pulse signals from the crank angle sensor 16 and the cam angle sensor 18 are read.

At a step S202, the cylinder member is discriminated in accordance with the crank pulse and cam pulse. At a step 27 1 1 S203, the crank pulse of the crank angle sensor 16 is discriminated in accordance with the cam pulse for detecting the angles BTDC 91 and 92.

At a step S204, the period fl.2 is calculated in accordance with the period tl.2 between the crank pulses discriminated at the step S203 and the angle (el - 92) M.2 = d t 1.2/d (91- 02)). At a step S205, the engine speed NI.2 is calculated in accordance with the period fl.2 (NI.2 <- 60/ (2 X - f 1. 2)).

At a step S206, the intake air quantity Q is calculated based on the output signal from the intake air quantity sensor 8.

At a step S207, the engine load Tp is calculated in accordance with the engine speed NI.2 and the intake air quantity Q (Tp <--K x Q/N1.2). At a step S208, the basic ignition timing 6B is derived from the lookup table mPeB in accordance with the engine speed NI.2 and the intake air quantity Q as parameters.

At a step S209, the knock control value eNK is set corresponding to the output signal from the knock sensor 19.

At a step S210, the vehicle speed and the output signal of the idle switch 96 are read. At a step S211, the idling state is determined. When the vehicle speed is not zero and the idle switch 96 is turned off, the driving state of the vehicle is determined and the program goes to a step S212. When the vehicle speed is zero and the idle switch 96 is 28 k turned on, the idling state is determined. The program goes to a step S213.

At the step S212, the basic igniticn timing OB is corrected with the knock control value eNK to calculate the ignition timing GIG.

At the step S213, the learning correcting coefficient LADVi of the corresponding cylinder NoA determined in the combustion condition estimating program is read. At a step S2141 the basic ignition timing GB is corrected with the knock control value 9NK and the learning coefficient LADVi to calculate the ignition timing OIG (eIG (--E)B + 9NK + LADVi).

At a step S215, the ignition time A-DV is provided in accordance with the ignition tiining OIG calculated at the step S212 or S214 and the period fl.2 calculated at the step S204 (ADV (-- 91G x fl.2).

At a step S216, the ignition time ADV is set in the timer. At a step S217, the timer starts measruing time in accordance with the angle signal e2 as a trigger signal. At - ignition time, a a step S218, when the timer reaches a se6,6 spark signal is applied to the ignitor 25.

In the ignition timing control systeem at the idling of the engine, the basic ignition timing is corrected with the learning cbrrecting coefficient which is used for estimating the 29 i combustion condition. Thus, the engine speed at idling becomes constant, thereby remarkably reducing fluctuation of the engine speed.

In order to estimate the combustion condition, the mean speed difference at non-working period of each cylinder is obtained based on the speed difference between before and after the combustion in the cylinder and the mean speed difference is compared with the fixed upper and lower limit values. Therefore, factors of the other cylinders are not included, the combustion condition is accurately detected.

In particular, the crank angle for detecting the engine speed during the detecting period in the non-working state is common to every cylinder so that the load exerted on the control unit can be reduced.

is Referring to Figs. 9 to 11 showing the second embodiment, the same structure and steps as the first embodiment are identified with the same reference numerals as Figs. 2 and 7 and the descriptions thereof are omitted.

In the second embodiment, the combustion condition is estimated in accordance with an angular acceleration of the engine.

Referring to Fig. 9, a combustion condition estimating section 52 comprises an angular acceleration calculator 52a to which the engine speed N NEW from the engine speed calculator 41d is applied for calculating an angular acceleration (dN/dt)NEW. When the idling of the engine is 1 determined at the idling state determining means 41e, an angular acceleration difference calculator 52b reads an angular acceleration (dN/dt)NEW calculated at the calculator 52a, and reads an angular acceleration (dN/dt)OLD stored in a predetermined address of the memory (RAM) 34, which is calculated in the last routine. The calculator 52b calculates an angular acceleration difference 6(dN/dt)i of the corresponding cylinder No. i discriminated at the cylinder discriminating means 41a in accordance with the difference between the angular acceleration (dN/dt)NEW and (dN/dt) OLD ( A (dN/dt) i = (dN/dt) NEW (dN/dt) OLD).

The angular acceleration (dN/dt)NEW is stored in the memory 34 to update the angular acceleration (dN/dt)OLD ((dN/dt)OLD-- (dN/dt)NEW).

The angular acceleration difference A (dN/dt) i is applied to a mean angular acceleration difference calculator 52c in which a mean angular acceleration difference A(dN/dt) Ai at the detecting period for the corresponding cylinder No. i is calculated in accordance with the angular acceleration difference A(dN/dt)i and the last mean angular acceleration difference A(dt)Ai(-1) stored in a predetermined address of the memory 34 through the weighted mean by the equation as follows.

A(dt)Ai = ((2 r _ 1) x A (dN/dt)Ai (-1) + A(dt)i)12 r 31 where r is weighted coefficient.

The mean angular acceleration difference at first time is zero.

The mean angular acceleration difference A(dt)Ai is calculated at every detecting period for the respective cylinders.

The calculating operation which will be described hereinafter is performed based on data for each cylinder.

The mean angular acceleration difference A(dt)Ai is applied to a.combustion condition estimating means 52d having fixed upper limit determining means 52e and fixed lower limit determining means 52f. The mean angular acceleration difference A(dt)Ai is compared with a fixed upper limit angular acceleration difference A(dN/dt)u is which is previously provided in the means 52e. When A(dNIdt)Ai A(dN/dt)u, the mean angular acceleration difference L(dt)Ai is compared with a fixed lower limit angular acceleration difference A(dNIdt)L which is previously provided in the means 52f.

These upper and lower fixed limit values L(dN/dt)u and A(dNIdt)L are determined based on the upper and lower determining values of the indicated mean effective pressure obtained by an experiment.

When A(dt)Ai > A(dt)L at the fixed lower limit determining means 52f, namely the mean angular acceleration difference A(dt)Ai is within the range of the fixed 32 1 limit angular acceleration difference ( L (dN/dt) u > A (dN/dt)Ai > A (dN/dt) L), a signal is applied to mean angular acceleration difference update means 52g. The update means 52f operates to update the last mean anc..ular acceleration difference A (dN/dt) Ai (-1) stored in the memory 34 with the mean angular acceleration difference A (dN/dt)Ai, A (dN/dt)Ai(-1) - A(dt)Ai.

If LADVi LmtRTD or LADVi > LmtADV is determined at the learning coefficient retard angle and the advance angle limit determining means 43e and 43f, the signal is applied to the mean difference update means 52g for resetting the mean angular acceleration di f ference A (dN/dt) Ai ( A (dN/dt) Ai t- 0). Thus, the update mans 52g operates to update the last mean angular acceleration difference A(dN/dt)Ai(-1) in the memory 34 by the reset means angular acceleration difference A (dN/dt) Ai ( A (dN/dt) Ai (-1) <-- 0).

The learning correcting coefficient update means 43g is applied with the signals from the fixed upper limit determining means 52e and the fixed lower limit determining means 52f of the combustion condition estimating means 52d. When A(dN/dt)Ai> 25(dN/clt)u at the means 52e, i.e. the combustion condition is extremely good, the learning correcting coefficient LADVi is corrected to retard with the crank angle C. The update means 43g operates to update the learning coefficient LADVi with the retarded coefficient (LADVi -LADVi - C).

33 i When A(dt)Ai < A(DN/ft)L at the fixed lower limit determining means 52f, i.e. the combustion condition is bad, the learning coefficient LADVi is corrected to advance with the crank angle C. The coefficient LADVi is updated with the advanced coefficient (ALDVi -LADVi + C).

The operation of the system for estimating the combustion condition of the cylinder at idling of the engine is described hereinafter with reference to the flowchart of Fig. 10. The control program is executed on each individual cylinder.

At the steps S101 to S106, the same programs as the first embodiment are executed. After the engine speed N NEW is calculated in accordance with the frequency f23 (N NEW <601(2 7T - f2.3) at the step S106, the program goes to a step S301 where the angular acceleration (dN-Idt)NEW is calculated in accordance with the engine speed N NEW.

At a step S302, in accordance with the difference between the angular acceleration (dN/dt)NEW and the angular acceleration (dN/dt)OLD calculated in the last routine, the angular acceleration difference A(dNIdt)i in the non-working period (Fig. 11) is calculated ( A (dN/dt)i 4- (dN/dt)NEW (dN/dt)OLD). At a step S303, the angular acceleration (dN/dt)OLD stored in the memory is updated with the angular acceleration (dN/dt)NEW ((dN/dt)OLD (dNIdt)NEW).

34 At a step S304, the mean angular acceleration A(dN/dt)Ai is calculated through the weighted mean based on the angular acceleration difference A(dN/dt)i and mean angular acceleration difference AW/dt)M(-1) in the last routine ( A(dt)Ai -((2 r _ 1) x A(dN/dt)Ai(-1) + A(dW12 r).

At a step S305i the mean angular acceleration difference A(dN/dt) is compared with fixed upper limit angular acceleration difference A(dN/dt)u. When A(dt)Ai >A (dN/dt)u, it is determined that the combustion condition is extremely good. The program goes to the steps S111 to S113 where the learning correcting coefficient LADVi is updated in the same programs as the first embodiment.

is On the other hand, at the step S305, when A (dN/clt)Ai 6(dN/dt)u, the program goes to a step S306 where the mean difference AldN/dt)Ai is compared with the fixed lower limit A(dN/dt)L. When A(dN/dt)Ai< 25 (dNIdt)L, it is determined that the combustion condition is bad. The program goes to steps S115 to S117 where the learning correcting coefficient LADVi in the RAM 34 is updated in the same programs as the first"embodiment.

At the step S306, when A(dt)Ai > A(dNIdt)L, it is determined that the mean angular acceleration difference A (dN/dt)Ai is in the range (dNIdt)u > A (dN/dt)Ai > A (dN/dt)L), the program proceeds to the step S308.

At a step S307, the last mean angular acceleration difference A(dt)Ai is reset ( A (dN/dt)Ai f 0).

At the step S308, the last mean angular acceleration difference A(dt)Ai (1) stored in the RAM is updated with the mean angular acceleration difference A(dt)A1 calculated at the step S304 or reset at the step S307.

The operation for controlling the ignition timing is the same as the first embodiment.

The correlation between engine speed and angular acceleration is shown in Fig. 11. In the secon d embodiment, the combustion condition is estimated In accordance with the angular accel(ration obtained by the engine speed through time differential. Thus, the time element is added, and hence accuracy of the system is further improved.

Referring to Figs. 12 and 13 showing the third embodiment, the same structure and steps as the first embodiment are identified with the same reference numerals as Figs. 2 and 7 and the descriptions thereof are omitted.

In the third embodiment, the combustion condition is estimated in accordance with a periodic phase (cycle) of the engine operation.

Referring to Fig. 12, a combustion condition estimating section 62 comprises a period difference calculator 62a which calculates a period difference Afi(i=1,3,2,4) of the corresponding cylinder at the idling of the engine. When the idling of the engine is determined at the idling state determining means 41e, the calculator 62a reads period f2.3 36 NEW calculated at the period calculator 41c, and reads period f2.3 OLD stored in the memory 34, which is calculated in the last routine. The calculator 62a calculates the period difference Afi of the corresponding cylinder No. i in accordance with the difference between the periods f23 NEW and f23 OLD ( Afi = f23 NEW <--f2.3OLD).

The period f.23 NEW is stored in the memory 34 to update the period f 2. 3 OLD (f 2. 3 OLD (- f 2. 3 NEW).

The period difference Afi is applied to a mean period difference calculator 62b in which a mean period difference AfAi at the detecting period for the corresponding cylinder No. i is calculated in accordance with the period difference fi and the last mean period difference 6fAi(-1) stored in the memory 34 through the weighted mean by the equation as 15 follows.

A fAi 2 r _ 1) x A fAi (-1) + A f i) /2 r The mean period difference at first time is zero.

The mean period difference AfAi is calculated at every detecting period for respective cylinders.

The mean period difference AfAi is applied to a combustion condition estimating means 62c having fixed lower limit'determining means 62d and fixed upper limit determining means 62e. The mean period difference AfAi is compared with a fixed lower limit period difference AfL which is previously provided in the means 42d.

37 i When A fAi > A fL at the fixed lower limit determining means 62d, the mean difference A fAi is compared with a fixed upper limit period difference A fu which is previously provided in the means 62e.

Since the period f is an inverse number of the engine speed, the fixed upper and lower limits of the period are inversely determined from those of the engine speed. When AfAi < Afu, namely the mean period difference AfAi is within the range of the fixed limit period difference ( A fL A fAi A fu), a signal is applied to mean period difference update means 62f. The update means 62f operates to update the last mean period difference AfAi (-1) stored in the memory 34 with the mean period dif f erence A fAi ( A fAi I- fAi).

If LADVi < LmtRTD or LADVi LmtADV is determined at the learning coefficient limit determining means 43e, or 43f, the mean period difference update means.62f is applied with the signal for resetting the mean period difference AfAi( AfAi f- 0). Thus, the last mean period difference AfAi (-1) in the memory 34 is updated by the reset means period di f ference A fAi ( A fAi (- 1) (- 0).

Signals from the fixed lower limit determining means 62d and the fixed upper limit determining means 62e are applied to the learning correcting coefficient update means 43g.

38 When A fAi:> A f L at the fixed lower limit determining means 62d, i.e. when the combustion condition is extremely good, the update means 43g operates to update the learning coefficient LADVi with the retarded learning coefficient which is corrected to retard with the crank angle C (LADVi LADVi - C).

When AfAi< tfu at the upper limit determining means 62e, i.e. when the combustion condition is bad, the learning correcting coefficient LADVi is updated with the advanced learning coefficient which is corrected to advance with the crank angle C (LADVi (- LADVi + C).

Describing the operation for estimating the combustion condition at idling state, referring to Fig. 13, at the step S105, the period f23 is calculated.

is At a step S401, in accordance with the difference between the period f2.3 NEW and the period f23 OLD calculated in the last routine, the period difference A fi in the non-working period is calculated ( Afi <- f2.3 NEW f23 OLD). At a step S402, -the period f2.3 OLD stored in the memory is updated with the period f23 NEW (f23 OLD f23 NEW).

At a step S403, the mean period difference AfAi is calculated through the weighted mean based on the period difference Afi and the means period difference AfAi (-1) in the last routine ( AfAi (-((2 r _ 1) x AfAi (-1) + Afi) /2 r).

39 At a step S404, the mean period difference A fAi is compared with the f ixed lower limit A fL. When A fAi< A fL, it is determined that the combustion condition is extremely good. The program goes to the steps S111 to S113 where the learning correcting coefficient LADVi is updated.

On the other hand, at the step S404, when AfAi > A fL,, the program goes to a step S405 where the mean period dif ference A fAi is compared with the fixed upper limit Mu. When A fAi > A fu, it is determined that the combustion condition is bad. The program goes to the steps S115 to S117 where the learning correcting coefficient LADVi is updated.

At the step S405, when A fAi < Afu, it is determined that the mean period difference AfAI is in the range fL A fAi < A fu), the program proceeds to the step S407.

At a step S406, the mean period difference AfAi is reset ( AfAi ig-0).

At the step S407, the last mean period difference AfAi (-1) stored in the RAM is updated with the mean period difference A fAi calculated at the step S403 or reset at the step S406. in the third embodiment, the period is used for estimating the combustion condition so that the calculating process is reduced to reduce the calculating time. 25 Referring to Pigs. 14 to 16 showing the fourth embodiment, the same structure and steps are identified with the same reference numerals as Pigs. 2 and 7 and the descriptions thereof are omitted.

In the fourth embodiment, the combustion condition is estimated in accordance with an angular velocity of the engine.

Referring to Fig. 14, the input data calculating section 41 is provided with an angular velocity calculator 41g to which the signal from the crank angle signal discriminating means 41b is applied. The calculator 41g measures the elapsed time t12 between the crank angle Cl of the projection 15a and the crank angle e2 of the projection 15b. The angular velocity w 1.2 is calculated in accordance with the elapsed time tl.2 and the included angle (Cl - 92) (wl.2 td(el-e2)/dtl.2). Then, the elapsed time t2.3 between the crank angle e2 of the projection 15b and the crank angle G3 of the projection 15c is measured. The angular velocity w 2.3 is calculated in accordance with the elapsed time t2.3 and the included angle (02-e3) ( w23 d(e2 - e3)Idt2.3). An angular velocity signal is applied to the engine speed calcul.ator 41d for calculating the engine speed N1.2 based on the angular velocity wl.2 (N1.2 = 60 A. 21 (2 7t-,) The ignition time setting means 43i of the ignition timing calculating section 43 is applied with the ignition timing eIG and the angular velocity wl.2 calculated at the angular velocity calculator 41g. The means 43i operates to 4 is set an ignition time ADV in accordance with the ignition timing E)IG and the angualr velocity w 1. 2 (ADV = eIG/ w 1. 2).

The combustion state detecting section 72 comprises an angular velocity difference calculator 72a which calculates an angular velocity di f ference A w i (i = 1, 3, 2, 4) of the corresponding cylinder at the idling of the engine. When the idling of the engine is determined, the calculator 72a calculates the angular velocity difference A w i of the corresponding cylinder No. i in accordance with the difference between the angular velocities w23 NEW and w23 OLD (Awi =w 2.3 NEW -w2.3 OLD).

The angular velocity w23 NEW is stored in the memory 34 to update the angular velocity w 2.3 OLD ( w 2.3 OLD 4(w23 NEW).

The angular velocity difference A w i is applied to a mean angular velocity calculator 72b in which a mean angular velocity difference Aw Ai at the detecting period for the corresponding cylinder No. i is calculated in accordance with the angular velocity di-fference Aw i and the last mean angular velocity difference Aw Ai(-1) stored in the memory 34 through the weighted mean by the equation as follows.

AwAi = (( 2 r _ 1) x A w Ai (-1) + A w i) 12 r The mean angular velocity difference at first time is zero.

The mean difference AwAi is calculated at every detecting period for the respective cylinders.

42 The mean angular velocity difference AwAi is applied to a combustion condition estimating means 72c having fixed upper limit determining means 72d and fixed lower limit determining means 72e. The mean difference AwAi is compared with a fixed upper limit angular velocity difference Aw u at the means 72d and compared with a fixed lower limit difference Aw L at the means 72e, respectively.

When A W U > A w Ai >A wL, the mean angular velocity difference AwAi is within the range of the fixed limit difference. The update means 72f operates to update the last mean difference Aw Ai (-1) stored in the memory 34 with the mean di f ference A w Ai ( A w Ai (-1) (-- A w Ai).

The update means 72f operates to update the last mean angular velocity difference Aw Ai(-1) in the memory 34 by the reset mean angular velocity difference Aw Ai, if LADVi < LmtRTD or LADVi > LmitADV is determined at the learning coefficient limit determining means 43e or 43f (Aw Ai (-1) ( 0) - When &o Ai >A w u at the means 72d, and when A w Ai< A w L at the means 72e, the update means 43g operates to update the learning coefficient LADVi with the corrected learning coef f icient (LADVi fLADVi - C or LADVi + C) in the same manners as the f irst embodiment.

Describing the operation, referring to Fig. 15, at the step S104, the crank pulses at the crank angles BTDC e2 and e3 are discriminated.

j 43 At a step S501, the angular velocity w2.3 is calculated in accordance with the elapsed time t2.3 between crank pulses discriminated at the step S104 and the included angle (e2 - e3) ( w23 -d(e2 - G3)/dt23).

At a step S502, in accordance with the difference between the angular velocities w23 NEW and W2.3 OLD, the angular velocity difference Aw i in the non-working period is calculated (A w i (- w23 NEW - w 2.3 OLD). At a step S503, the angular -velocity w 2. 3 OLD stored in the memory isupdated with the angular velocity w 2. 3 NEW ( w 2.3 OLD w 2.3 NEW).

At a step S504, the mean angular velocity difference,6wAi is calculated through the weighted mean based on the angular velocity difference A wi and the mean angular velocity difference AwAI(-1) in the last routine (AWAI((( 2 r _ 1) x A w Ai (-1) + A w i) /2 r).

At a step S505, the mean difference Aw Ai is compared with a f ixed upper limit dif ference AA) u. When &,3 Ai> A w u, it is determined that the combustion condition is extremely good. The p2ograrn goes to the steps S111 to S113 for updating the learning correcting coefficient LADVi.

On the other hand, at the step S505, when AwAi Aw u, the program goes to a step S506 where the mean difference AwAi is compared with the fixed lower limit difference L. When &Ai<twL, it is determined that the combustion 1 1 A 44 condition is bad. The program goes to the steps S115 to S117 for updating the learning coefficient.

At the step S506, when AwAi =5 A wL, it is determined that the mean a, ngular velocity difference A w Ai is in the range (A wu =5 A wAi 6 wL), the program proceeds to the step S508.

AT a step S507. the mean difference A wAi is reset Caw Ai - 0).

At a step S508. the last mean angular velocity difference A w'Ai(-1) stored in the RAM is updated with the mean angular velocity difference A wAi calculated at the step S504 or reset at the step S507.

Referring to Fig. 8, in the operation for controlling the ignition timing, at step S203, the crank pulse is discriminated.

At a step S250. the angular velocity wl.2 is calculated in accordance with the elapsed time tl.2 between the crank pulses discriminated at the step S203 and the angle (el - G2) (wl.2 -d (91 - e2)ldtI.2). At a step S251, the engine speed N1.2 is calculated in accordance with the angular velocity wl.2 ( N1.2 <--(6012 Z) x wl.2)).

At a step S260, the ignition time ADV is provided in accordance with the ignition timing GIG calculated at the step S212 or S214 and the angular velocity wl.2 calculated at the step S250. (ADV (-eIG1 wl.2).

In the fourth embodiment, since the angular velocity is used, the calculating time is also reduced.

The system of the present invention may be employed for the other engines such as a four-cycle single-cylinder engine, a four-cycle two-cylinder engine, a four-cycle three-cylinder engine, two-cycle single-cylinder engine, and a two-cycle two-cylinder engine, because the combustions of the cylinders are not overlapped with each other.

The mean value of the difference of engine speed, angular acceleration, period, or angular velocity, each of which is correlated with the combustion condition of the cylinder, is compared with the fixed upper and the lower limit values. Thus, the combustion condition is determined as the absolute quantity so that the combustion condition of the corresponding cylinder can be accurately estimated.

The combustion condition is estimated on the basis of the signals from the sensors provided on the engine. The cost of the parts is reduced,- and the system can be used for the conventional engines.

The ignition timing is accurately controlled in dependency on the combustion condition of the corresponding cylinder. in particular, the engine speed at the idling state is stable, thereby reducing the noise and vibration of the engine.

A 46 While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.

is X 47

Claims (7)

Claims:

1. A system for detecting the condition of the combustion in a cylinder of an internal combustion engine, said engine having a crank angle sensor for producing a crank angle signal representing the angular position of the crankshaft of the engine and a cam angle sensor for producing a cam angle signal representing the angular position of the camshaft of the engine, comprising detecting means for detecting a period before and a period after top dead centre of the cylinder in the expansion stroke and for producing signals representing said respective periods; detector means responsive to said period signals for detecting a parameter representing the motion of the engine during each of the periods and for producing for each of the periods a signal which represents said parameter, difference calculator means for calculating from said signals the difference in the parameter in the periods; a mean difference calculator for calculating a mean value of said differences; and means for comparing said mean value with predetermined limit values to determine the condition of the combustion in the cylinder.

2. A system for detecting the condition of the 48 combustion in each cylinder of a multi-cylinder internal combustion engine having a crank angle sensor for producing a crank angle signal representing the angular position of the crankshaft of the engine and a cam angle sensor for producing a cam angle signal representing the angular position of -the camshaft of the engine, comprising: discriminating means responsive to said cam angle signal for detecting in turn each cylinder in its expansion stroke and for producing a signal representing said cylinder; period detecting means responsive to said cylinder signal for detecting periods before and after top dead center of each cylinder in its expansion stroke, and for producing period signals representing said respective periods; detector means responsive to said period signal for detecting a parameter representing the motion of the engine during each of said periods and for producing respective condition signals; difference calculator means for calculating from the signals the difference in the parameter in said periods; a mean difference calculator for calculating a mean difference of said differences; and means for comparing said mean difference with predetermined limit values thereby determining the 49 condition of the combustion in the cylinder.

3. A system as claimed in claim 1 or 2 in which the parameter which is detected is the speed of the engine.

4. A system as claimed in claim 1 or 2 in which the parameter which is detected is the angular velocity of the crankshaft of the engine.

5. A system as claimed in claim 1 or 2 in which the parameter which is detected is the angular acceleration of the crankshaft of the engine.

6. A system as claimed in any preceding claim in which the ignition timing of the or each cylinder is adjusted, if necessary, to ensure that the mean value is within said limit values.

7. A system for detecting the condition of the combustion in the or each cylinder of an internal combustion engine substantially as herein before described with reference to the accompanying drawings.

Published 1991 at The Patent Office. State House. 66/71 High Holborn. L4DndonWCIR47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent-